The solenoid side seizes up with corrosion on that one. Search for the thread on how to strip it down and do it (it's from a vauxhall forum initially -same valve). Basically drill a 3mm hole in the end of the plastic case and drift out the assembly carefully. Put a screw in the hole on reassembly to fill it in.
Don't be too scared of doing it, it's quite easy but make sure you can't lose the internals while you're pulling it apart
Doubt you'll gain any advantage by unplugging it - it'll just stay in the position it's stuck in, IF it's stuck of course. You can't blank it off without registering a fault on the mjet models but you CAN get a perforated blanking plate that reduces the amount of gas / soot going through the EGR system.
Try and avoid cleaning the MAF just yet. Try the EGR first.
have you checked all the hoses (intake, vacuum etc) for splits as well? bear1 is right about the MAP as well - mine was choked up.